MADIX agent on protonated diallylammonium monomer cyclopolymerization with efficient chain transfer to monomer

Journal Pre-proofs Impact of the RAFT/MADIX agent on protonated diallylammonium monomer cyclopolymerization with efficient chain transfer to monomer Yulia A. Simonova, Maxim A. Topchiy, Marina P. Filatova, Natalia P. Yevlampieva, Mariya A. Slyusarenko, Galina N. Bondarenko, Andrey F. Asachenko, Mikhail S. Nechaev, Larisa M. Timofeeva PII: DOI: Reference:

S0014-3057(19)31712-4 https://doi.org/10.1016/j.eurpolymj.2019.109363 EPJ 109363

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European Polymer Journal

Received Date: Revised Date: Accepted Date:

22 August 2019 25 October 2019 9 November 2019

Please cite this article as: Simonova, Y.A., Topchiy, M.A., Filatova, M.P., Yevlampieva, N.P., Slyusarenko, M.A., Bondarenko, G.N., Asachenko, A.F., Nechaev, M.S., Timofeeva, L.M., Impact of the RAFT/MADIX agent on protonated diallylammonium monomer cyclopolymerization with efficient chain transfer to monomer, European Polymer Journal (2019), doi: https://doi.org/10.1016/j.eurpolymj.2019.109363

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Impact of the RAFT/MADIX agent on protonated diallylammonium monomer cyclopolymerization with efficient chain transfer to monomer Yulia A. Simonovaa, Maxim A. Topchiya, Marina P. Filatovaa, Natalia P. Yevlampievab, Mariya A. Slyusarenkob, Galina N. Bondarenkoa, Andrey F. Asachenkoa, Mikhail S. Nechaeva, Larisa M. Timofeevaa* a A.V.

Topchiev Institute of Petrochemical Synthesis, RAS, Leninsky prosp. 29, Moscow, 119991 Russia [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected] b Saint

Petersburg State University, Universitetskaya nab. 7/9, Saint Petersburg, 199034 Russia [email protected]

Abstract We have studied applicability of reversible addition-fragmentation chain transfer /macromolecular design via the interchange of xanthate (RAFT/MADIX) method to radical cyclopolymerization of protonated diallylammonium monomer, namely diallylammonium trifluoroacetate (DAATFA), occurring with efficient chain transfer to monomer reaction. The latter drives to a significant extent polymerization, noticeably setting molecular weight, МW, of polymers and their polydispersity (polydispersity index (PDI) = 2.8-3.0). For the first time, upon DAATFA polymerization in presence of RAFT ethylxanthogenacetic acid (xanthate) in aqueous solutions at 70C, the side chain transfer reaction was inhibited and control of the polydispersity was achieved, the PDI = 1.2-1.3. The structural characteristic of poly(diallylammonium trifluoroacetate) (PDAATFA) polymers was analyzed via 1H and 13C NMR and IFS FTIR (ATR) spectroscopy. It was proved that the structure of polymers obtained by RAFT polymerization fully corresponds to the polymers PDAATFA containing cationic pyrrolidinium links and trifluoroacetate-counterions. At the optimal xanthate concentrations, the main products are polymers with the end dithiocarbonate group, i.e. macro-RAFT PDAATFA. Static/dynamic light scattering, viscometry and ultracentrifugation were used for polymers characterization. Molecular weight was determined by two independent methods: static light scattering (Mw) and hydrodynamic parameters analysis (MDη). The PDI Mw/Mn was calculated on the basis of Fujita approach, using the determined distributions of sedimentation coefficients. The experimental number average molecular weights, Mn, grow with polymerization time, 6700 g mol-1 < Mn < 10500 g mol-1, but did not correspond to the theoretical one. The rate of polymerization mediated by xanthate was shown to increase approximately twice in comparison to free-radical process that distinguishes DAATFA RAFT polymerization from other processes mediated by RAFT agent. Keywords Protonated diallylamine; Radical cyclopolymerization; Chain transfer to monomer; RAFT/MADIX polymerization; Xanthate; Protonated polydiallylamine; Narrow polydispersity

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1. Introduction1 Secondary and tertiary protonated diallylammonium (PDAA) polymers based on protonated monomers of diallylamine (DAA) series exhibit efficient antimicrobial activity against a rather broad range of hospital pathogens, including rarely-observed activity against M.tuberculosis mycobacteria [1,2]. Owing to these properties, protonated PDAAs are distinguished among quaternized diallylammonium polymers obtained by radial cyclopolymerization of quaternary diallylammonium salts [3-6]. The known cationic quaternized polymer, poly(diallyldimethylammonium chloride) (PDADMAC), is a polymer adsorbent employed as a flocculent to purify water at waste water treatment plants and at some production facilities (including paper) that to neutralize negatively charged colloid particles and diminish sediment size [7-9]. To resolve problems with polymerization of DAA monomers in a non-quaternized form, which are related to a degradative chain transfer to the monomer [10-13], a strategy has been proposed the key moment of which is to create in the polymerization media a dominant amount of the monomer in protonated form [14]. Competitive ability of the transfer reaction is reduced as a result, and the diallyl transfer radical is transformed into a chain propagation radical via intramolecular cyclization (efficient chain transfer) [14]. Based on the approach, methods were developed to synthesize protonated monomers, trifluoroacetate salts of the DAA series, and polymers on their basis. New water-soluble protonated secondary and tertiary polydiallylamines, trifluoroacetate polydiallylammonium salts, have been obtained; kinetics of the process has been studied and the bi-molecular mechanism of the termination, i.e. recombination of macroradicals, has been demonstrated (Scheme 1) [15-17]. Related to prospects for the development of new bactericide materials based on protonated PDAA polymers is the issue of how free-radical polymerization can be controlled to obtain polymers with a specified molecular weight and rather narrow molecular weight distribution (MWD). Before early 2000s and during last two decades, several main approaches and techniques have been developed to control free-radical polymerization that enable the synthesis of macromolecules with predictable weight and narrow MWD [18-31]. Nitroxide-mediated polymerization (NMP) has been reported and used to control styrenic-based (co)polymers synthesis [18, 19]. Atom transfer radical polymerization (ATRP) (transition metal-catalyzed living radical polymerization) was developed independently by Sawamoto [20] and DAA - diallylamine; PDAA – poly(diallylamine); PDADMAC - poly(diallyldimethylammonium chloride); DAATFA - diallylammonium trifluoroacetate; PDAATFA – poly(diallylammonium trifluoroacetate) 1

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Matyjaszewski [21, 22] with co-workers for styrenic and (meth)acrylate-based monomers. Somewhat later, a controlled polymerization technique has been developed that includes the reversible addition-fragmentation chain transfer (RAFT) process [23–31]. The RAFT-polymerization method has advantages compared to NMP and ATRP, since it is applicable to a broader range of monomers, may be used in various solvents (including water [2628]), and tolerates a broad set of conditions [26-32]. Recent developments related to the use of monomers of two different functionalities in cyclopolymerization processes and also advances in new initiating systems and polymerization catalysts enabled the precision syntheses of polymers with regulated cyclic structures by highly regio- and/or stereoselective cyclopolymerization. These processes can be activated by means of radical, ionic, or transition-metal mediated chain-growth polymerization mechanisms [33]. Development of the RAFT/MADIX method, macromolecular design via the interchange of thiocarbonylthio compounds (xanthates) as RAFTagents, enabled controlled polymerization of nonconjugated monomers, including N-vinyl monomers [34, 35]. The latter compounds feature high reaction capacity of propagation radicals and, at the same time, involvement in a side reaction of chain transfer in the process of polymerization [32, 34, 35]. RAFT agents xanthates seem to be more suitable to control radical cyclopolymerization of protonated diallylammonium monomers. The propagation radicals of these monomers don’t possess a very high reaction ability like vinyl monomers propagation radicals, and, as it is pointed out above, the polymerization occurs with a significant kinetic contribution of the efficient chain transfer to monomer that noticeably affects molecular weight and polydispersity of the polymers [15-17] (see Scheme 1). For example, for polymerization of diallylammonium trifluoroacetate (DAATFA), the transfer constant См.= 3.810-3 at 30С [17]. Given this framework in the work, we examine applicability of the RAFT/MADIX method to DAATFA cyclopolymerization. Choice of the RAFT/MADIX agent was limited, in particularly, by solubility of xanthates in an aqueous solution of the hydrophilic DAATFA. Xanthate ethylxanthogenacetic acid was used as the RAFT agent. Radical cyclopolymerization of DAATFA monomer in the presence of the RAFT agent may be schematically represented as follows in Scheme 2. After general initiation, propagating chain Pm is formed (1.1). Pm can interacts with H atom of -CH2 group of DAATFA that leads to formation of dead polymer with the end -CH3 group and propagating chain I with the end CH2=CH- group (reaction (1.2), a frequency of the chain 4

transfer to monomer is determined by transfer constant to monomer, Schemes 1 and 2) [15-17]. In presence of RAFT-agent according to the proposed mechanism for the RAFT-polymerization [23-32, 34, 35], when a propagating radical Pm adds to RAFT-agent, an intermediate radical II is formed which may then fragment to produce polymer III with the end dithiocarbonate group and a new radical R(COOHCH2 in the case of RAFT xanthate, reaction (1.3)). The latter in turn reinitiates a new propagating chain IV (with the end COOHCH2- group in the given case, reaction (1.4)) involved then in establishing the main equilibrium (reaction (1.5)). This process allows achieving control in RAFT-mediated polymerization. In the given polymerization with efficient chain transfer to monomer, RAFT-agent may interact also with propagating chain of I species (reaction (1.6)). It may lead to formation of polymer VIII with the end vinyl and dithiocarbonate groups. Thus in the presence of RAFT agent, the direction in which DAATFA polymerization may develop is determined by competition between two possible chain transfer reactions: efficient chain transfer to monomer (1.2) and reversible chain transfer based on the addition-fragmentation mechanism performed by the RAFT-agent (1.3) (Scheme 2). The primary goal of the study was to kinetically suppress the efficient chain transfer to monomer (1.2) by means of competitive reaction (1.3). It would enable RAFT-agent to control the chains propagation process. The purpose of the work was thus to obtain PDAA polymers with quite low МW and a rather narrow polydispersity. The option to implement such an approach in radical polymerization with an inherent kinetically significant chain transfer to monomer is of importance not only for production of polymers with required characteristics in practical applications, but also is of academic interest. 2. Materials and methods 2.1. Materials Trifluoroacetic acid (TFA, for synthesis, ≥99.0%; Merck, Germany) and initiator 4,4¢-azobis(4-cyanovaleric acid) (ACVA, 98.0%; Aldrich) were used without additional purification. Reagent DAA (for synthesis, 97%; Acros, Belgium), and solvents, hexane and diethyl ether of analytical

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grade (Khimmed, Russia), were distilled before use. For chromatographically pure monomer DAA, Тb = 111–112°С. 1H NMR (Me2CO-d6):  = 3.20 (d, 4 H, 2 -CH2, J = 5.89 Hz), 5.12 (м, 4Н, 2-СН2), 5.87 (м, 2Н, 2-СН). 2.2. Synthesis RAFT agent. Ethylxanthogenacetic acid (xanthate) was synthesized according to [36]. 1H NMR NMR (CDCl3): δ 4.66 (q, 2H), 3.98 (s, 2H), 1.43 (t, 3H); 1H NMR NMR (D2O): δ 4.62 (q, 2H), 3.90 (s, 2H), 1.33 (t, 3H) (Supplementary material, Fig. 1). Diallylammonium trifluoroacetate (DAATFA). Monomer salt DAATFA was prepared from DAA and TFA as described in detail elsewhere [1, 16,17]. The DAATFA salt, which precipitated in hexane as white crystals, was in each case washed several times with hexane to remove unreacted amine and TFA; residual hexane was removed using a rotor evaporator. The yield was 85-89 %. The structure of the salt was confirmed by elemental analysis and 1Н NMR spectra. The degree of amine protonation in solutions of the DAATFA salt was assessed by the characteristic weak-field shift of signals from the protons in the -СН2 group in the 1Н NMR spectra, since the Н atoms of the α-СН2 group proved to be the most sensitive to protonation of the amine [15,16]. DAATFA, 1H NMR (Me2CO-d6):  = 3.71 (d, 4 H, 2 -CH2, J = 6.43 Hz), 5.47 (m, 4Н, 2-СН2), 6.00 (m, 2Н, 2СН). PDAATFA Polymers. Polymers were synthesized in the presence of the RAFT agent xanthate as follows. Radical polymerization of DAATFA was carried out in aqueous solutions with initiator 4,4¢-azobis(4-cyanovaleric acid) (ACVA), [ACVA] = 510-3 mol L-1, at several concentrations of the RAFT agent: ratios of [xanthate]/[ACVA] concentrations was 2; 3; 6. DAATFA (10.575 g, 2 mol L-1) and xanthate (0.068 g, 1.510-2 mol L-1, corresponding to the [xanthate]/[ACVA] = 3) was dissolved in a small amount of bidistilled water; next, initiator ACVA (0.035 g, 510-3 mol L-1) and bidistillate were added until the entire volume was 25 ml (pH of solution was 2.5). An ampoule with a solution was degassed six to seven times in a vacuum setup to 3 × 10–3 mm Hg under freezing with liquid N2, sealed, and thermostated. The polymer was precipitated into Et2O and purified three times via reprecipitation from MeOH solution into Et2O. The prepared polymer was dried over P2O5 under a vacuum.

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2.3. Measurements The HSQC and 13C NMR spectra of polymers were measured using a Bruker AVANCE 600 spectrometer at 303 K. The 1Н NMR spectra were also measured with a MSL-300 Bruker spectrometer (300 MHz). NMR spectra of the studied polymer samples are shown in Figs. 1 and Fig.2. The IR spectra of dried PDAATFA samples were recorded by attenuated total reflectance (ATR) with a Bruker IFS FTIR spectrometer – 66 v/s vacuum (range 600 - 4000 cm-1, cryst. Ge, 100 scans, resolution 2 cm-1). The IR spectra of the studied polymer samples are shown in Figs. 3, 4. Elemental analysis was carried out by the dynamic flash combustion method (Dumas combustion method). Results of the elemental analysis of S are given in Table 1 and in the text. 2.4. Determination of molecular weight of polymers The synthesized samples were characterized in 1М NaCl, i.e. under high-ionic strength condition, to exclude possible influence of polyelectrolyte effects [15,17]. The solutions were prepared directly in 1М NaCl within a day. The solvent had the following characteristics at a temperature of 298 K: density ρ0 =1.036 g/cm3, viscosity η0=0.975 cP, and refraction index n0 = 1.3501. Two methods were applied to determine molecular weight of the synthesized samples. First of them is the classical method of static light scattering in polymer solution that allows determining weight-average molecular mass Mw [37], and the second method is based on using hydrodynamic invariant A0 [38, 39]. The latter parameter allows the molecular mass MDη to be determined through experimental measurement of translation diffusion coefficient D0 and intrinsic viscosity [η] of macromolecules in a solution. The coefficients of diffusion were obtained by examining dynamic light scattering in polymer solutions [37]. Both static and dynamic light scattering were studied using a “PhotoCor Сomplex” facility (“PhotoCor”, Russia)2 at a temperature of 298 K maintained with an accuracy of 0.05 К. A 25-mW laser operated at a wavelength of λо = 445 nm was used as the light source. The intensity of scattered light was measured in a range of scattering angles θ = 400–1400. Measurements of static and dynamic light scattering, as well as sedimentation rates were performed using the equipment kindly provided by the Resource Center of St. Petersburg State University “Center of Diagnostics of Functional Materials for Medicine, Pharmacology, and Nanoelectronics”. 2

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Zimm plot [37] was applied to analyze static light scattering data. The Mw value was obtained using Debye equation (1). Нс/I(0, c)= 1/Mw +2A2c

(1)

Here the intensity of light scattering I(0, c) corresponds to the Rayleigh ratio determined for each solute concentration c at scattering angle θ →0, Н = 4π2n02(dn/dc)2/NАλ04 is the scattering constant, n0 is the refraction index of the solvent, dn/dc is the refraction index increment of the polymer solution, NA is the Avogadro constant; and А2 is the second virial coefficient. The A2 value estimated from Zimm plots of the studied samples was A2= (3.7 ±0.5) 10-4 cm3 mol g-2. This value of the second virial coefficient indicates that 1 M NaCl is a thermodynamically “good” solvent for polymers under investigation. Similar A2 values were reported for PDAATFA series obtained by free-radical polymerization [39]. An Abbemat WR/MW refractometer (“Anton Paar”, Austria) with an accuracy of ±0.0001 was used to determine refraction index n in polymer solution as a function of concentration. Refraction index increment, dn/dc, was determined as the slope of linear dependence (n – no) = f(c). The autocorrelation functions of scattered-light determined in the dynamic light scattering mode of the “PhotoCor” facility were processed using the “DynаLS” software [40]. This program is intended to analyze distributions of particles in solutions by relaxation time τ. Translation diffusion coefficients of macromolecules D were found using Eq. (2): 1/τ = Dq2

(2),

where q =(4πno/λо) sin (θ/2) is the scattering vector. As follows from Eq. (2), D is the slope of dependence 1/τ = f(q2). The value of D0 was found as D0 = lim с →0 D. Hydrodynamic radius Rh of macromolecules was calculated using Stokes-Einstein equation (3): Rh = kT/6πη0D0

(3),

where k is the Boltzmann constant, Т is the absolute temperature, and η0 is the solvent viscosity. An automated viscometer Lovis-2000 M/ME (“Anton Paar”, Austria), which operates based on the Höppler method, was used to measure viscosity. The intrinsic viscosity [η] of polymers was determined, using the Huggins method, by graphic extrapolation of the reduced viscosity ηsp/с to zero 8

solute concentration [41]. Huggins constants k´ were varied in the 0.4-0.5 range typical of “good” solute-solvent systems. The obtained [η] values are displayed in Table 2. Having such characteristics of macromolecules as Dо and [η], Eq. (4) below that defines hydrodynamic invariant А0 [38] may be employed to calculate molecular mass MDη: А0= (η0D0/T)(MDη[η]/100)1/3

(4)

The value A0= 3.0х10-10 erg/K mol1/3 experimentally found for the PDAATFA series synthesized by free-radical polymerization [39] and Eq. (4) were used to calculate MDη. The obtained values of Dо, Rh, and molecular masses Mw and MDη for the samples under study are contained in Table 2. 2.5. Molecular-weight distribution of polymers Ultracentrifugation technique was used to compare molecular mass distributions of PDAATFA samples synthesized by different methods. Sedimentation of macromolecules in 1M NaCl was studied using a Beckman analytical ultracentrifuge ProteomeLab XL-I Protein Characterization System at a rotor speed rate of (40–55) × 103 rpm; an AN-60Ti four-cell titanium rotor was employed in measurements. Sedimentation process was recorded with a Rayleigh interference optical system using a red laser (655 nm) as a light source. Sedimentation-layer scans were processed with the use of the Sedfit programs [42]. Concentration dependencies of sedimentation coefficients s were determined for the several solute concentrations of the samples in the range (0.02-0.08)10-2 g cm-3 with the purpose to obtain Mark-Kunh-Houwink (M-K-H) equations between the sedimentation coefficient s0=limc0 s and molecular weight Mw for the samples belonging to all three sets. The extended Fujita approach [43, 44] was used for determination of Mw/Mn, polydispersity index (PDI), for polymers synthesized by the RAFT polymerization. This approach is based on transforming a quasi-continuous distribution g(s) of sedimentation coefficient s into a distribution of molecular weight, f(M), for linear structure polymers using the relation f(M) = g(s) · (ds/dM) and a scaling relation between s and M, i.e. M-K-H type 9

equations [44]. The functions g(s) were derived from the scans processing by means of Sedfit program [42]. The possibility of PDI evaluation based on the study of macromolecules sedimentation in analytical ultracentrifuge has been shown for different classes of polymers [44-47]. The received Mw/Mn values are listed in Table 2. 2.6. Kinetic study by 1Н NMR spectroscopy Kinetic studies were performed using 1H NMR spectroscopy in much the same way as it was done in [17]. 1Н NMR spectra were measured using an MSL-300 Bruker spectrometer (300 MHz). We used the calibration dependencies for the (DAATFA + PDAATFA) modeling mixtures, which have been determined in [17], to relate the change in the intensity of signals due to Н atoms to changes in concentrations of the monomer and polymer. Thin ampoules, d~1.5-2 mm, with polymerization solution were used in the experiment. The sealed ampoule containing the polymerization solution was heated in a thermostat; polymerization was stopped several times at specified intervals, and the ampoule was frozen in liquid nitrogen and immersed in the standard ampoules with a deuterated solvent (D2O) for spectrometer measurements. The standard error in determination of integral intensities in the 1Н

NMR spectra was 5%. The relative error in determination of the time of polymerization in kinetic dependences, which was calculated from the ratio

of the overall time of spectrometric experiment conducted n times (n  10 min) and the overall time of polymerization, was ~3%. Since in 1H NMR spectra, signals due to the monomer were not fully separated from the neighboring signals related to the polymer, conversion of DAATFA was estimated as accumulation of PDAATFA polymer. The latter was evaluated based on the intensity integral of the signal due to H atoms in (C3,4-cis)H2 groups, which was fully separated in 1H NMR spectra of the polymerization solutions (Fig. 1), using calibration dependencies [17]. All the experiments were repeated 4-5 times. The results of the kinetic study are shown in Fig. 7. 3. Results and discussion 3.1. Structure of polymers

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Polymers, which differed by duration of polymerization, were separated and analyzed for three reaction series: [xanthate]/[ACVA] were equal to 2, 3, and 6. All polymers belonging to the first two series have been studied; in the latter case, only two polymers synthesized during 20 h and 25 h could be analyzed (if polymerization continued for a longer time, polymerization process proved to be almost completely suppressed, while a negligible amount of the polymer has been obtained after a 15-hour-long process). Fig. 1 shows 1Н NMR spectra of PDAATFA polymers, the first of which was obtained in free-radical polymerization (Fig. 1a), and two other were synthesized in the presence of the xanthate agent with different ratios [xanthate]/[ACVA] (Fig. 1b,c). When the ratio [xanthate]/[ACVA] was equal to 3 or 6 (characteristic spectrum is shown in Fig. 1b), the 1Н NMR spectra of all produced samples contains signals due to protons of the xanthate agent hydrogen carbon groups that may be associated with the end group of the polymer. The quartet in the 3.5- 3.7 ppm range and triplet in the 1.1-1.2 ppm range are related to protons in the СН2- and СН3- groups, respectively, may be considered as signals of the end thiocarbonylthio group СН3-СН2-О-C(-S-)=S (compare to Supplementary material, Fig. 1). Signals of the end vinyl group (Fig. 1a and Fig. 2), that are characteristic of free radical polymerization of DAATFA involving efficient chain transfer to monomer (Scheme 1) [1, 15-17], are virtually not observed in these spectra (Fig. 1b). Otherwise, the spectra of the polymers produced in the presence of the RAFT agent for the ratio [xanthate]/[ACVA] = 3 and 6 are identical to the spectrum of PDAATFA polymer synthesized by free-radical polymerization (compare to Fig. 1a). Structure of PDAATFA polymers with the end dithiocarbonate groups was confirmed by IR Fourier spectroscopy (Fig. 3a). Spectra of the three samples, one of which (P1 – sample 1) was synthesized without the RAFT agent, fully correspond to the structure of the PDAATFA polymer containing pyrrolidinium cationic links and trifluoroacetate-counterions. Broad bands associated with ammonium cation are observed in the 27602503 cm-1 range. Trifluoroacetate anion bands: valence oscillations C=O (1668 cm-1) are shifted toward shorter wavelength with respect to valence oscillations of carboxylate ions (1600 cm-1) due to trifluoroacetic substituent; there are also corresponding valence and deformation oscillations in the О=С-О node at 1123 cm-1, and valence oscillation of С-F bond (1196 cm-1). Samples 2 (P3) and 3 (P0) apparently contain the end dithiocarbonate group. The presence of that group is indicated by the 1053 cm-1 band due to valence oscillations of S=С bond, increased and modified intensity of bands in the 600-700 cm-1 region characteristic of valence oscillations of S-С bonds, and modified relations between intensities in the 1123 cm-1 region. It is of importance that intensity of oscillations of double С=S bonds in IR 11

spectra correlates with the content of S that follows from elemental analysis (Table 1). Data on intensity were obtained from an analysis of IR spectra of five PDAATFA samples (Fig. 3b), one of which (sample 1) was synthesized without the RAFT agent and other in the presence of the xanthate agent. Spectra of samples 2-5 contain the band 1053 cm-1 associated with С=S bonds whose spectral intensity depends on the specific sample; in addition, the spectrum in the 600-700 cm-1 range characteristic of valence oscillations of S-С bonds is modified. These spectra are reduced to the common baseline and normalized using the 1425 cm-1 band related to the -СН2 group in the cycle, i.e. the band that is the least sensitive to chain length and conformation of polymer. This band may be used as an internal standard for semi-qualitative estimates of the content of polymer end groups. The spectra shown in Fig. 3b were used to assess in semi-quantitative terms the content of end С=S bonds. In Table .1, there are listed normalized intensities of the 1053 cm-1 band (C=S) (with respect to the intensity of the internal 1425 cm-1 standard) that are correlated with the content of sulfur in the samples determined from elemental analysis. Good correlation between the intensity of the С=S band oscillations and content of sulfur in the sample of these polymers is clearly seen. The conducted analysis enables a conclusion that DAATFA polymerization in the presence of xanthate for the ratio [xanthate]/[ACVA] = 3 and 6 occurs primarily according to reactions (1.1), (1.3), and (1.5) that correspond to growth and reversible chain transfer to the RAFT agent, while efficient chain transfer to monomer (reaction (1.2)) is mainly kinetically inhibited (Scheme 2). As a result of reinitiation by radical R in the reaction (1.4), polymers should be produced with end СООН-СН2- group. Signals from the hydrogen atoms belonging to this end group are usually observed in 1Н NMR spectra in the 1.5-2 ppm region and are therefore included in signals of hydrogen in С6,7(cis, trans) skeletal atoms. Thus, if xanthate concentration is 1.510-2 or 3.010-2 mol L-1 and [xanthate]/[ACVA] = 3 or 6, the main products of DAATFA polymerization are polymers of structures III and VI with the end dithiocarbonate group that may be considered as macro-RAFT PDAATFA (Scheme 2). The well-defined signals of these end groups indicate short polymer chain and small molecular weight of the polymers (it will be considered below). The signals of the end dithiocarbonate group did not disappear even after repeated re-precipitating the sample with Et2O and were still observable for polymers which were stored at room temperature or in D2O solution through four-five months. After this period, signals of the dithiocarbonate group were not longer registered in 1H and 13C NMR spectra of those polymers or their D2O solutions, while the structure of the polymer chain retained 12

during a year for dry polymers and about two years in D2O solutions (see Supplementary material, Fig.2). The lability of the thiocarbonylthio group and postpolymerization of RAFT-polymers are known and different techniques for these groups modification were suggested [48]. If xanthate concentration is lower, [xanthate]/[ACVA] = 2 and [xanthate] = 1.010-2 mol L-1, 1Н NMR spectra of polymers contain signals due to the end vinyl groups, 5.5-6.1 ppm, while signals related to the end dithiocarbonate groups are not observed, a characteristic spectrum is displayed in Fig. 1с). In Fig. 4a, IR spectra of PDAATFA polymers from series 3, namely samples 6 and 7 (polymers P10 and P11, respectively), are compared with spectrum of sample 1 (P1) synthesized by free-radical polymerization and sample 3 (P8) spectrum with maximal normalized intensity of the 1053 cm-1 band (C=S) (the maximum number of the dithiocarbonate groups). The apparently expected band due to С=S bond in the 1053 cm-1 range is missing in the spectra of samples 6 and 7. These spectra are however closer to the spectrum of sample 3 rather than 1, especially in the absorption region of S-С bonds. Details of these spectra in the region of 1053 cm-1(С=S) and 680 cm-1 (S-С) bands with the baselines set across the wings of those bands are presented in Figs. 4b and 4c. Fig. 4b clearly shows that С=S bonds are present in samples 6 and 7, but their content is more than an order of magnitude smaller in comparison with sample 3. As it is seen in the Fig. 4c, in the samples 3, 6 and 7 spectra, there is almost complete disappearance of the band 635 cm-1 which is characterized for the polymers obtained by free-radical polymerization (sample 1). The band due to S-С bonds (680 cm1)

unfortunately overlaps with the band of the polymer itself located at 675 cm-1. Spectra of samples 6 and 7 exhibit however a change and increase in

intensity in the 680-700 cm-1 region albeit weaker than in the sample 3 spectrum. This is a convincing argument in favor of the presence of S-С bonds in polymers 6 and 7. A comparison of the spectra of samples 6 and 7 with that of sample 3 in the regions 1053 cm-1 and 680 cm-1 enables a conclusion that the content of S-С bonds in the two former polymers is significantly higher than that of С=S bonds. This observation is presumably indicative of the formation of products based on the stable radical RAFT adducts of structures V, or/and VII (see Scheme 2). The data quoted above show that if [xanthate]/[ACVA] < 3 (xanthate concentration is lower than 1.5 mol/L), both the paths of chain transfer, i.e. efficient chain transfer to monomer (1.2) and reversible addition transfer to the RAFT agent (1.3), are realized (Scheme 2). In this case, the polymerization occurs according to the reactions (1.1) – (1.6). The products include polymers of structure I (similar to ones for free-radical polymerization) and, apparently, a small amount of III, VI and VIII polymers (the content of these polymers with the end dithiocarbonate groups is an order of magnitude smaller than in the case where the [xanthate]/[ACVA] ratio is 3 or 6). Supposedly, there is some amount of polymers based on the 13

RAFT adducts V, or/and VII containing S-C-S bonds in the structure, fraction of which is significantly higher than that with the end dithiocarbonate groups (Scheme 2).

3.2. Molecular weight distribution of polymers and PDI Studying ionogenic polymers and especially polysalts frequently involves applying non-standard exploration methods, a situation that was noted, in particular, in [28, 44-47, 49]. No adequate conditions for applying chromatographic methods have been found as yet for water soluble PDAATFA samples that contain bulky trifluoroacetate-anion. The most reliable information is provided in such cases by so-called absolute methods for determining molecular weight (MW). One of them is the method of static light scattering in solutions [37] that we have used in our study. The results for Mw presented in Table 2 are indicative of strong influence of the conditions of synthesis on the molecular weights of the samples synthesized in the presence of the RAFT agent. It should be noted that the selected “polymer-solvent” system features for samples obtained with xanthate an insignificant increment of refraction index dn/dc=(0.11±0.01) cm3 g-1. This circumstance significantly affects the accuracy with which Mw is determined by the static light-scattering method in the case of polymers whose weight is less than 104 g mol-1 [37]. Another method of determination of the molecular weight was also used for that reason that yielded MDη values. This method is based on physical principles that are quite different from those underlying light scattering: namely, it employs two hydrodynamic parameters of macromolecules in solution determined in an independent way [38]. Polymer derivatives of diallylammonium were shown in [39] to feature hydrodynamic properties that correspond to flexible-chain polymers. It was verified that the value of the hydrodynamic invariant A0 in their aqueous solutions is typical of suchlike (presented in the methodical part of the study.) It should be noted that small values of hydrodynamic radiuses Rh (Table 2) are also indicative of flexible PDAATFA polymer coils being heavily twisted in 1М NaCl.

14

The MDη values calculated using Eq. (4) and experimental values of D0 and [η] agree well with the Mw values obtained by the absolute method. Also, the MDη values better correlate with changes in synthesis conditions than Mw. Changes in MDη of the samples show that molecular weight of polymers in the presence of the RAFT agent significantly decreases in all experimental series; the magnitude of this decrease depends however on the concentration of the RAFT agent and polymerization time (see Table 2). The molecular weights of the samples produced in the presence of xanthate in series 1 are 4 to 8 times smaller (depending on polymerization time) than molecular weight of polymer P14 synthesized without the RAFT agent under same conditions and of virtually all PDAATFA polymers obtained by free-radical polymerization in an aqueous solution under various conditions. (In free-radical polymerization, along with the usual dependence of PDAATFA molecular weights on concentrations of monomer and initiator, there is distinguishable dependence on temperature that is due to changes in relative competitive ability of the chain transfer to monomer reaction [15-17]). The molecular weights of polymers obtained in series 3 are two-three times higher than in series 1, albeit smaller than in free-radical polymerization. Obviously, higher molecular weight is one of the reasons, along with the small amount of macro-RAFT polymers, of that the signals of end dithiocarbonate groups are not visible in the 1H NMR spectra of polymers of series 3. It is interesting to compare molecular weights Mw listed in Table 2 with Mw values estimated from the sulfur content: Sample

P2

P3

P4

P5

P6

P7

S, %

0.76

0.64

0.55

0.45

0.39

0.48

8.3

9.9

11.5

14.1

16.3

13.2

Mw10-3, g mol-1

Correlation is quite satisfactory if take into consideration errors which can give flash combustion method, i.e. 10-15%. Molecular weight of polymer is related to its hydrodynamic parameters in solution such as hydrodynamic size, coefficients of translational and rotational diffusion, and sedimentation coefficient [38]. Distributions of polymer molecules by hydrodynamic parameters may be considered therefore 15

equivalent to molecular-weight distributions (MWD). Information about the width of distribution by molecular parameters is provided by the dynamic light-scattering method. Fig. 5 presents typical distributions of scattered-light intensity as a function of molecule size in solution. Comparison of Figs. 5a and 5b clearly shows that using RAFT xanthate significantly narrows distributions by molecule size in solution and therefore decreases width of the polymer MWD in comparison to the PDAATFA samples obtained by free-radical polymerization. This is also evidenced by comparison of distributions C(s) by sedimentation coefficients displayed in Fig. 6 for the samples produced using xanthate agent and by free-radical polymerization. It may be concluded that the RAFT agent xanthate significantly reduces the width of polymer MWD in all experimental series. If concentration of the RAFT agent is optimal (for the cases under study [xanthate]/[ACVA] = 3), so the effect of the side reaction of efficient chain transfer to monomer is virtually negligent, PDI of the samples diminishes to 1.2-1.3 in the entire polymerization area (Table 2). This is in remarkable contrast to the high polydispersity for free-radical polymerization of the DAATFA (PDI = 2.8-3.0). Interestingly, even if efficient chain transfer to monomer is involved in polymerization as we can see by products is series 3 ([xanthate]/[ACVA] = 2), the RAFT agent heavily affects molecular weight and especially PDI which is decreased to 1.3-1.5 (Table 2). 3.3. Kinetics of polymerization Importantly, molecular weight of polymers obtained in series 1 grows as polymerization time increases. Experimental Mn values determined as Mn = MDη/PDI (taking into account closeness of MDη to Mw) can be compared to theoretical molecular weight Mn,th calculated via known eq (5). Mn,th = {([M]0 MWmon)/([RAFT]0 - [I]t )} + MWRAFT,

(5)

[I]t = 2f [I]0(1 – exp(-kd/t))

(6)

16

In eq (5), [I]t - concentration of initiator derived chains to the moment of time t (6), [M]0, MWmon, , [RAFT]0, f, [I]0, kd, t, and MWRAFT represent the initial monomer concentration, molecular weight of the monomer, conversion, initial RAFT concentration, initiator efficiency, initial initiator concentration, rate constant for initiator decomposition, time, and the molecular weight of the RAFT, respectively. [I]t member, i.e. concentration of initiator derived chains, was included in the calculations of Mn,th via eq 5. Even if we assume low efficiency of initiator ACVA, f = 0.5, magnitudes of [I]t are smaller but comparable with the xanthate concentration [RAFT]0 especially at t > 5 h which is the time of approximately half-decomposition of ACVA at 70C [50] (Supplementary materials, Table 1). Thus, it would be incorrect to neglect [I]t member in the process which occurs at 70C for such a long reaction time. As it is seen in Fig.7a, the behavior of molecular weight with monomer conversion is not linear: there is positive deviation after ~20% conversion (~20 h); experimental Mn values do not correspond to the Mn,th ones obtained via eq (5), being higher than Mn,th. However, a low polydispersity is observed. This indicates the incomplete control of the polymerization. Similar behavior was observed in the study of RAFT polymerization of DADMAC with initiator ACVA and xanthate/MADIX [28]. The pseudo-first-order kinetic plot is non-linear, it has downward curvature after 10 h (Fig. 7b). There are two reasons for the non-linear dependence. As it was shown, the kinetics of the radical polymerization of DAATFA, as well of its CH3-N-substituted homolog, is not first-order with respect to the monomer (it has the higher order when [M] > 1 mol L [15, 16, 51]). Along with this, it should assume a decrease in the concentration of propagating radicals, especially if take into consideration that decomposition of ACVA is 72 % to 10 h as calculated based on kinetic data [50]. Comparison of the rates of monomer conversion for two free-radical polymerization of DAATFA initiated by ACVA and APS at the similar concentrations of the initiators and monomer within 5 h of polymerization (till half-decomposition of ACVA) displays slow initiation rate by ACVA (Fig. 7c). The rate of monomer conversion upon polymerization initiated by APS at 50C is approximately three times higher than with ACVA at 70C. The low initiation rate by ACVA as compared to APS was discussed earlier [28]. When considering free-radical polymerization with initiator ACVA and the RAFT polymerization mediated by xanthate at the same conditions, it should be inferred that presence of the RAFT agent accelerates monomer conversion which becomes approximately two times higher (Fig. 7c). Supposedly, there are two reasons for this result. Firstly, there is a negligible contribution of the chain transfer to monomer (that is confirmed by the 17

absence of end vinyl group and low polydispersity). The side reaction (1.2) (Scheme 2) results in formation of the dead polymer and transfer diallyl radical. This process, albeit leading to transformation of the transfer diallyl radical to the propagation one, significantly retards polymerization, especially at high temperatures due to increase in the competitive ability at 70C. In contrast upon RAFT polymerization, in reaction (1.3), new initiator R is obtained together with macro-RAFT polymer III (and then macro-RAFT VI) possessing high reactivity (Scheme 2). At the same time, formation of the radical RAFT adducts II and V leads to a retardation of the polymerization rate depending on a stability of the intermediate adducts determined by the equilibrium constant K = k-/k in the -scission reactions (1.3) and (1.5) [52]. Thus, the observable acceleration of the DAATFA polymerization mediated by xanthate is the result of several noted factors. This distinguishes RAFT polymerization of protonated DAA monomers from polymerization of e.g. DADMAC mediated by RAFT xanthate: the rate of the latter is slightly retarded by comparison with the free-radical process that is related to a certain lifetime of the RAFT adduct radicals [28]. In series 3, (in which xanthate concentration was not enough to prevent completely from the chain transfer to monomer reaction), products of DAATFA RAFT polymerization contained some amount of the polymers with SC-S bonds in the structure that might be obtained based on the stable RAFT adducts V or/and VII (Scheme 2). This result is not yet understood. The other distinguishing characteristic is the necessary condition to retain positive charge on the DAA monomer. The retention of proton equilibrium in the polymerization medium is the crucial factor for that radical polymerization of the protonated salt DAATFA (or its N-substituted homolog) can occur without degradation [14-17]. To this end, the absence of salt admixtures in aqueous solution is one of the most important requirements for retaining proton equilibrium during the polymerization process. It was shown that presence of even standard electrolytes admixtures in distilled water (obtained in a stainless steel distiller) in concentration of 10-2-10-4 mol L-1, which is comparable with the concentration of active hydrogen ions in the DAATFA polymerization solutions (рН 2.5), leads to partial disturbance of proton equilibrium resulted in increase in the constant chain transfer to monomer and decrease in Mw of PDAA polymers by comparison to polymerization in bidistillate (obtained in quartz distiller) [17]. In PDAATFA aqueous solutions in 1M NaCl, a violation of the proton equilibrium affects the thermodynamic conditions for the PDAATFA macrochain in the solution resulting in a significant difference of the hydrodynamic dimension of the macromolecules and their translational and rotational mobility in solution, and also the viscosity and diffusion properties in comparison to those of PDADMAC molecules in the same solvent [39]. Also due to the above reason of possible deprotonation, DAATFA (or its N-substituted homolog) solutions are very susceptible to increase in pH value of solution. 18

The low yield in the case of free radical polymerization of DAATFA with ACVA (Fig. 7c) is related to several factors: a large contribution of the chain transfer to monomer at 70C, low rate of initiation by ACVA in combination with moderate reactivity of propagating radicals. Upon free radical polymerization of DAATFA with APS at 50C initial rate of polymerization, VDAATFA, was (1.77 0.23)10-5 mol L-1 s-1 [17]; the monomer conversion achieved about 70% during 50 h. For comparison, upon polymerization of diallyldimethylammonium trifluoroacetate (DADMATFA, quaternized homolog), VDAMATFA, with APS and monomer at the same concentration, initial rate was 6.610-5 mol L-1 s-1 at 60C [5]. Thus, the value of VDAATFA is about three times lower than VDAMATFA at the comparable conditions. Obviously, this is due to the contribution of the chain transfer to monomer and a lower propagation rate upon DAATFA polymerization in comparison to DADMATFA. It correlates with the data on DAATFA and DADMAC conversions for RAFT/xanthate polymerization in presence of ACVA: conversion is about 12% for DAATFA during 6 h, 70C (Fig. 7 c), while it was 21% for DADMAC during the same time, 60C [28]. If polymers with the end dithiocarbonate group, i.e. macro-RAFT are the main products in the RAFT polymerization of DAATFA, it means that rate of chain transfer by macroradical to another monomer ((1.2) Scheme 2) is small in comparison with the reaction of RAFT agent addition to the macroradical ((1.3) Scheme 2). This condition is met by the relation between rates of the RAFT addition and chain transfer to monomer reactions (7):

kadd·[RAFT][Pm] > km·[M]][Pm] = Cm·kp·[M]][Pm]

(7)

It can be written in the forms (8) and (9): kadd·[RAFT] > Cm·kp·[M],

(8)

[RAFT] > Cm·[M]·kp/kadd,

(9)

where Cm = km/kp. It is evident that the relations (8) and (9) are easy met if Cm < 10-4. In the current polymerization, Cm = 3.810-3 at 30С [17]. It is simple to evaluate Cm at 70С considering that the value of Cm depends on the difference ∆E between activation energies of competitive propagation and chain 19

transfer to monomer reactions (preexponential factors of these reactions are approximately equal) [14-16]: Cm = exp(-∆E/RT) = 7.310-3. From (9), the lower limit for the RAFT agent concentrations at [M]0 = 2 mol L-1 and 70С is given by: [RAFT] > 1.4610-2 kp/kadd mol L-1 . From the experimental data, the limit concentration is 1.510-2 mol L-1. It follows from (9) that the lower limit for the RAFT agent concentration should increase with an increase in [M] concentration that to inhibit the side chain transfer to monomer reaction. At the same time, excess concentration of the RAFT agent might lead to violation of balance between number of propagating macroradicals and concentration of RAFT agent (especially considering small rates of initiation in the case of ACVA and also moderate reactivity of the diallylammonium macroradicals) and as a result to suppression of chain propagation. Therefore along with the lower limit, an upper one for the RAFT agent concentration range should be. As we can see from a very small polymer yield, which decreases with a time of polymerization, xanthate concentration becomes excess if [xanthate]/[ACVA] = 6. At the concentration [xanthate] = 310-2 mol L-1 polymerization is suppressed. Thus to inhibit the side chain transfer to monomer reaction and to retain chain propagation in the RAFT polymerization of DAATFA mediated by xanthate at the given values of [M]0, [ACVA]0 и T, the required range for RAFT xanthate concentration is limited by 3 ≤ [xanthate]/[ACVA] < 6. Conclusion Upon DAATFA cyclopolymerization in the presence of RAFT/MADIX agent ethylxanthogenacetic acid (xanthate), the side chain transfer to monomer reaction is inhibited and control of the polydispersity is achieved, the PDI = 1.2-1.3 in the entire polymerization area in aqueous solutions at 70C. This is a remarkable contrast to the PDI equal to 2.8-3.0 upon free-radical polymerization of DAATFA. But the experimental Mn values albeit increase with polymerization time, do not correspond to the theoretical ones. The rate of DAATFA polymerization mediated by xanthate is increased approximately twice by comparison with the free-radical process. This confirms suppression of the side chain transfer reaction and distinguishes DAATFA RAFT polymerization from other RAFT processes which occur without/with small kinetic contribution of the inherent chain transfer to monomer reaction. 20

Thus, the main goal of the work is achieved and the desirable polymers with quite small Mw and narrow polydispersity are obtained. The further study on improvement of DAATFA RAFT polymerization process, in particular via a variation of conditions including a RAFT-initiator pair, will allow obtaining PDAATFA with a higher yield during a smaller polymerization time. We believe that on the basis of macro-RAFT PDAATFA and/or its copolymers, new materials can be obtained that might find applications especially in biomedical field. Acknowledgements Authors are very grateful to Prof. Alexandr S. Shashkov (IOC RAS) for their help in two-dimensional HSQC and 13C NMR study of polymers. This work was carried out within the State Program of TIPS RAS. Data availability The raw/processed data required to reproduce these findings cannot be shared at this time due to legal or ethical reasons as well time limitations.

21

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Captions to figures Fig. 1. 1Н NMR spectra of polymers PDAATFA: (a) - sample P1 (free radical polymerization, Mw 73000 g mol-1), Bruker AVANCE 600, 303 K, D2O; chemical shifts are given relative to the internal standard TMS (δH = 0.0 ppm), signals due to hydrogen atoms of macrochain are assigned using the two-dimensional HSQC spectrum [17] and

13C

NMR (Fig. 2), range δH = 5.5–6.0 ppm corresponds to the signals due to the terminal vinyl group

СН2=СН-; (b) – sample P3 ([xanthate]/[ACVA] = 3, t=20 h), MSL-300 Bruker spectrometer (300 MHz), D2O, there are evident signals due to the end dithiocarbonate groups CH3-CH2-O-C(=S)-S-: quartet (3.52-3.50 ppm) and triplet (1.19 ppm); (c) – sample P10 ([xanthate]/[ACVA] = 2, t=20 h), Bruker AVANCE 600, 303 K, D2O, there are signals of the end vinyl groups but no evident signals due to the end dithiocarbonate groups. Fig.2. 13C NMR spectrum of polymer PDAATFA, sample P1, Bruker AVANCE 600, 303 K, D2O, signals are assigned based on 13C NMR spectrum of poly(N,N-diallyl-N-methylammonium trifluoroacetate) [1] and poly(N,N-diallyl-N-methylamine) [15].

Fig. 3. IR spectra (ATR) of PDAATFA polymers: (a) - 1 – sample P1 (free radical polymerization, initiator ACVA, Mw 73000 g mol-1), 2 - sample P3 ([xanthate]/[ACVA] = 3, t=20 h), 3 - sample P0 ([xanthate]/[ACVA] = 6, t=20 h); (b) - the samples 1 and 2 in the case (a), 3 - sample P8 ([xanthate]/[ACVA] = 6, t=25 h), 4 – sample P5 ([xanthate]/[ACVA] = 3, t=30 h ), and 5 – sample P7 ([xanthate]/[ACVA] = 3, t=40 h). complete disappearance of the band 635 cm-1 which is characterized for the polymers obtained by free Fig. 4. IR spectra of the samples PDAATFA: (a) - 1 and 3 - the samples in the case Fig.3b, 6 – sample P10 ([xanthate]/[ACVA] = 2, t = 20 h, and 7 sample P11 ([xanthate]/[ACVA] = 2, t = 25 h; (b) – details of the spectra in case (a), region of 1053 cm-1(С=S) band with the baselines set across the wing of this band: in the IR spectra of the samples 6 and 7, intensity of the band 1053 cm-1 is more than an order of magnitude lower than the one in the spectrum of the sample 3; (c) – details of the spectra in case (a), region 680 cm-1 (S-С) band with the baselines set across the wing of this band: in the

27

spectra of the samples 3, 6 and 7, there is almost radical polymerization (sample 1), spectra of samples 6 and 7 exhibit a change and increase in intensity in the 680-700 cm-1 region albeit weaker than in the sample 3 spectrum. Fig. 5. Normalized distribution of scattered-light intensity as a function of molecule size: (a) - solution of sample P6 ([xanthate]/[ACVA] = 3, t = 35 h) in 1М NaCl with a concentration of с=110-2 g cm-3, scattering angle 90; (b) - solution of a polymer sample obtained by free-radical polymerization, initiator APS, 70C. Fig. 6. Normalized distributions С(s) by sedimentation coefficients s (expressed in Svedberg units) obtained, using the Sedfit program [42], for various samples prepared with initiator ACVA: (a) – samples P1 (1, free-radical polymerization) and P9 (2, [xanthate]/[ACVA] = 2, 15 h); (b) - samples P2, P8, and P7 obtained for various [xanthate]/[ACVA] ratios (see Table 2). Fig.7. Kinetics of DAATFA polymerization, initiator ACVA, RAFT agent xanthate, [ACVA] = 510-3 mol L-1, [xanthate]/[ACVA] = 3 (series 1), T=70C, pH = 2.5, monomer conversion was set equal to polymer accumulation estimated based on intensity integral of the signals due to H atoms in (C3,4-cis)H2 groups of polymer link in 1H NMR spectra of the polymerization solutions (considering the calibration coefficient [17]), standard error 10%, relative error in time determination – 3%. (a) - pseudo-first-order kinetic plots; (b) - dependence of Mn and Mw/Mn on monomer conversion; (c) – DAATFA conversion vs time: 1 – RAFT-polymerization, series 1, 2 – free radical polymerization with ACVA ([ACVA] = 510-3 mol L-1, T=70C), 3 and 4 – free radical polymerization with initiator ammonium persulfate, [APS] = 510-3 mol L-1, T=40C and 50C accordingly [17]. Scheme 1. Cyclopolymerization of protonated diallylammonium monomers: paths 1 and 3 - chain propagation, kp; path 2 - chain transfer to monomer, km, with subsequent transformation of the diallyl transfer radical into a chain propagation radical by means of intramolecular cyclization.

28

Scheme 2. Basic reactions of cyclopolymerization of DAATFA (initiator - 4,4¢-azobis(4-cyanovaleric acid, ACVA), that occurs with efficient chain transfer to monomer, in the presence of reversible addition–fragmentation chain transfer (RAFT) agent (and : kp and km – the rate constants of propagation and efficient chain transfer to monomer reactions, kadd and k-add and k and k- - the forward and reverse rate constants of addition and fragmentation reactions, and ki – the rate constant of reinitiation.

29

Table 1. Content of S in the polymers obtained under various conditions and correlation with relative intensities of bands in C=S in the IR spectra of samples shown in Fig. 3b. D1053/D1423 a

S, %

-

0

20

0.16

0.64

19.0

6

25

0.34

1.26

15.7

P5/4

3

30

0.09

0.45

20.3

P7/5

3

40

0.11

0.48

23.2

Sample/number in Fig. 3b P1 b/1

[xanthate]/[ACVA] ratio -

t, h polymeriz.

P3/2

3

P8/3

a Normalized

Yield, %

intensities of the 1053 cm-1 band (C=S) with respect to the intensity of the internal 1425 cm-1 standard. b Sample P1 (No. 1 in Fig. 3a,b) is

prepared by free radical polymerization, [ACVA] = 10-2 mol L-1, T=50C, t = 60 h, Mw = 73000 g mol-1.

30

Table 2 Molecular weights (g/mol), hydrodynamic properties, and Mw/Mn (PDI) of PDAATFA samples in 1М NaCl a Rh, Mw MDη D0107, nm 10-3 10-3 cm2 s-1 Series 1 - [xanthate]/[ACVA] = 3

Sample

t, h

[η], cm3 g -1

((Mw/Mn) 0.1) b

Yield, %

P2

15

6.0±0.5

11.7±0.7

1.9

10±2

8.0

1.2

17.7

P3

20

6.4±0.5

10.7±0.7

2.1

10±2

9.0

1.2

19.0

P4

25

6.6

10.3±0.5

2.2

10±2

10.0

1.2

19.2

P5

30

6.8

9.7±0.8

2.3

10±2

11.4

1.2

20.3

P6

35

8.0

8.9±0.2

2.5

14±1

13.7

1.3

21.9

P7

40

7.8

9.0±0.5 2.5 14±1 13.6 Series 2 - [xanthate]/[ACVA] = 6

1.3

23.2

P8

25

4.8±0.5

11.7±0.7 1.9 8.0 Series 3 - [xanthate]/[ACVA] = 2

1.5

15.7

P9

15

9.8±0.7

7.2±0.5

3.1

25±2

21.1

1.3

16.1

P10

20

10.0

6.8

3.3

23.8±0.8

24.5

1.5

17.5

P11

25

11

6.7

3.3

24.2±0.8

23.3

1.5

18.1

P12

30

12±1

5.9±0.5

3.8

30±3

31.3

1.5

19.5

Free-radical polymerization c P13

50

20.0

3.6

6.2

85

48.7 31

P14

20

16.5

4.3

4.8

50

P1

60

19.3±0.8

3.8

5.9

73

72.9

2.8

9.1

3.0

27.2

aAll

experiments with RAFT agents were

carried out with initiator ACVA, [ACVA] =

510-3 mol/L, T = 70C. b Calculated on the basis of formalism [43, 44] using С(s) function and experimental power relation of Mark-Kunh-Houwink type between sedimentation coefficient and molecular weight for the samples of all three sets. c Free radical polymerization: P13 - initiator ammonium persulfate, [APS] = 10-2 mol/L, T = 30C [38]; P14 - [ACVA] = 510-3 mol/L, T = 70C; P1 – [ACVA] = 10-2 mol/L, T = 50C.

32

Fig. 1a.

33

Fig. 1b

34

Fig. 1c

35

Fig.2

36

Int.

C(O)O 1123

0,3

-

C(O)O

-

1668

CF

1196

0,2 +

N(R4)

-CH 2940

2760

C=S

0,1 C-S

2503

-OH

1053

3 2 1 -1 cm

0,0 1000

1500

2000

2500

3000

3500

Fig. 3a

37

0,6

Int.

0,4

0,2 1425 1053

0,0

5 4 3 2 1

910

1000

1500

2000

2500

3000

3500

cm

-1

Fig. 3b

38

#1 #3 #6 #7

Int. 0,6

0,3

0,0

cm 3500

3000

2500

1500

1200

900

-1

600

Fig. 4a.

39

Int.

#1 #3 #6 #7

0,04

0,03 1053

0,02

0,01

0,00

cm

-0,01 1040

-1

1060

Fig. 4b

40

0,03

#1 #3 #6 #7

Int.

0,02 680 635

675

0,01

0,00

cm 620

640

660

680

-1

700

Fig. 4c

41

а

b

Fig. 5.

42

C(s) 1.0

0.8

0.6

0.4

0.2

1

2 0

2

4

6

8

10

12

s, S

Fig. 6.

43

2,500

12000

2,300

10000

Mn

1,900 6000 1,700 4000

1,500

2000

1,300

0 0,175

Mw /Mn

2,100

8000

1,100 0,185

0,195

0,205 0,215

0,225

0,235

Conversion Mn exp

Mn theor

Mw/Mn

Fig. 7 a

44

0,30

0,25

ln([M]0/[M]t)

0,20

0,15

0,10

0,05

0,00 0

10

20

30

40

t, h

Fig. 7 b

45

25

C polymer, %

20 15 10 5 0

0

10

20

30

40

time, h 3 - APS - 40C

4 - APS - 50C

1 - ACVA-xanthate -70C

2 - ACVA -70C

Fig.7c.

46

+ N R

I

I, T, H2O

Pn

.

CH2 + N

+

H

H

H

R

R = H; CH3; C2H5

1, kp CH2

I[

2, km

CH2

H

Pn

.

Me

CH2

H

+ N

R

+

CF3COO¯

H

+ N

.

]n+1 CH2 + N

+ N

H

R

CF3COO¯

end group I

R

CF3COO¯

CF3COO¯

CF3COO¯

H

+ N

R

CF3COO¯

R

CF3COO¯

. end group

H

+ N

R

CF3COO¯

СH

3 kp



Pm

+ N

H R CF3COO¯

47

Scheme 1.

48

ACVA

xanthate: Z-C(=S)-S-R Z = O-CH2-CH3; R = CH2-COOH

49

kp

1.1. I + M → I-Mn ; I-M + M → Pm km

kp

1.2. Pm + M → Pm ─CH3 + {CH2═CH─M → CH2═CH─Pn} kadd



─S─C─S─R

kβ

I Pm─S─C═S + R │ III Z

1.3. Pm + S═C─S─R Pm k add k-β │ │ II Z Z k 1.4. R + M → COOH─CH2─Pl kadd IV kβ  1.5. Pl + S═C─S─Pm Pl─S─C─S─Pm COOH─CH2─Pl─S─C═S + Pm k-add k-β │ │ │ V VI Z Z Z -

i

1.6. CH2═CH─Pn + S═C─S─R │ Z

kβ

kadd

CH2═CH─Pn─ S─C─S─R CH2═CH─Pn─S─C═S + R k-add k-β VII │ VIII │ Z Z

│ 1.7.ZPm, Pn, Pl, R → dead polymers

Scheme 2.

│ Z ⇌

+



Pm

50

Declarations of interest: none.

51

Impact of the RAFT/MADIX agent on protonated diallylammonium monomer cyclopolymerization with efficient chain transfer to monomer Yulia A. Simonova, Maxim A. Topchiy, Marina P. Filatova, Natalia P. Yevlampieva, Mariya A. Sljusarenko, Galina N. Bondarenko, Andrey F. Asachenko, Mikhail S. Nechaev, Larisa M. Timofeeva

km I, T, H2O

H

H

kp

+ N

.

I-Pg -Me +

+ N

kp

CH2-CH-Pm

(1)

H

CF3COO¯

I-Pn (1)

H

CF3COO¯

I, T, H2O, Xanthate

km

S=C(Z)-S-R, kadd, k I-P

l

kp

Pf -S-C(Z)=S + Pl (2)

kri, kadd, k

C(s) 1.0

0.8

0.6

0.4

0.2

1

2 0

2

4

6

8

10

12

s, S

52

Highlights 

DAATFA radical cyclopolymerization involves efficient chain transfer to monomer



Via RAFT/MADIX process efficient chain transfer to monomer is inhibited



Via RAFT/MADIX process control of polydispersity is achieved



Rate of DAATFA RAFT polymerization increases in comparison to free-radical process



PolyDAATFA with narrow polydispersity in presence of xanthate

53